This is a design change required for (http://www.google-melange.com/gci/task/view/google/gci2012/8141202)

To make the application simple it was decided to store each time slot the user is selecting as a timestamp against the event and the user in the tbl_reponses table.

Therefore the selected output of the UI should be changed accordingly.

use JSON to pass the data to logic layer. You need to document the chosen JSON format and convention clearly so that others can refer to to it later.

Stick to UTC time always. Document assumptions on READ_ME.